background <-
function(xlim = c(24, 0), ylim = c(-50, 50), mag = 3, cex = 1, lab = FALSE, grid = FALSE, ...) {
  data(constellation)
  constellation <- constellation
  par(xaxs = "i", yaxs = "i")
  plot(constellation$RA, constellation$DEC, cex = log(constellation$MAG), col = "grey", xlab = "Right Ascension (h)", ylab = expression(paste("Declination", degree)), xlim = xlim, ylim = ylim, axes = FALSE, type = "n")

  rect(par("usr")[1], par("usr")[3], par("usr")[2], par("usr")[4], col = "skyblue")

  points(constellation$RA, constellation$DEC, cex = 0.2 * log(constellation$MAG), pch = 19, type = "l", col = "white")

  points(constellation$RA, constellation$DEC, cex = 0.2 * log(constellation$MAG), pch = 19, col = "white")

  ### abline(h = c(-60, -30, 0, 30, 60), v = seq(0,24,by = 3))
  abline(h = 0, v = 12)

  ### par(xaxs = "i", yaxs = "i")
  ### plot.default(0, 0, xlim = xlim, ylim = ylim, axes = FALSE, ...)
  axis(1, at = c(24, 21, 18, 15, 12, 9, 6, 3, 0), labels = c("24h", "21h", "18h", "15h", "12h", "9h", "6h", "3h", "0h"))
  axis(2, at = seq(-60, 60, by = 15), labels = c("-60", "-45", "-30", "-15", "0", "15", "30", "45", "60"))
  abline(v = 12)
  abline(h = 0)

  box()
}
